Nonaqueous electrolyte solution secondary battery

Details Nonaqueous electrolyte solution secondary battery Nonaqueous electrolyte solution secondary battery

2001-01-16

2004-10-19

Crepeau, Jonathan (Department: 1746)

Chemistry: electrical current producing apparatus, product, and

Means externally releasing internal gas pressure from closed...

Blowout type

C429S053000

Reexamination Certificate

active

06805991

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a safety valve and a nonaqueous electrolyte secondary battery using the same.
2. Description of the Related Art
In recent years, portable information devices such as lap-top computers and wordprocessors, AV devices such as camera integrated video tape recorders and liquid crystal television sets, and mobile communication devices such as portable telephones are remarkably developed. For batteries used as power supplies, secondary batteries having small sizes, light weights, and high energy densities are demanded. Until now, aqueous-solution-based secondary batteries such as a lead battery, a nickel-cadmium battery, and a nickel-hydrogen battery are used. These aqueous-solution-based secondary batteries sufficiently satisfy the demands related to light weights and high energy densities.
Recently, as clean batteries having high energy densities, nonaqueous electrolyte secondary batteries attract considerable attentions and are greatly expected.
A conventional nonaqueous electrolyte secondary battery will be described below with reference to
FIGS. 4A-C
to
6
.
FIG. 4A
is a sectional view showing a conventional nonaqueous electrolyte secondary battery (e.g., disclosed in Japanese laid-open patent publication No. 8-315798).
In the nonaqueous electrolyte secondary battery, an electrode element
2
is a cylindrical bottomed outer packaging can
1
holds an electrode element
2
therein, a nonaqueous electrolytic solution (not shown) is injected into the outer packaging can
1
, and the nonaqueous electrolytic solution soaks in the electrode element
2
.
The electrode element
2
is constituted such that a positive electrode and a negative electrode each formed by a mixture obtained by mixing an active material, a binder, and a conductor with a elongated current collector are laminated across a micro-porous separator as positive electrode and negative electrode, and the laminated structure is winded around, e.g., a cylindrical core in the form of a spirally coiled electrode.
The electrode element
2
is inserted into the outer packaging can
1
such that the leading side of a negative electrode lead
10
faces the bottom side of the outer packaging can
1
.
On both sides of the electrode element
2
, insulation plates are arranged, and free ends of the leads
9
and
10
of the electrode element
2
are led to the outside of the insulating plates. The free end of the negative electrode lead
10
is welded on the bottom surface of the outer packaging can
1
serving as an electrode terminal leading portion.
A lid
7
, a PTC element
3
, and a safety valve
6
are caulked on one end side of the outer packaging can
1
through a gasket
8
to seal one end of the outer packaging can
1
.
At the central portion of the safety valve
6
, a projecting portion
6
a
projecting toward the electrode element
2
is formed. The projecting portion
6
a
is welded on a sub-disk
4
welded on the free end of the positive electrode lead
9
. In this manner, the projecting portion
6
a
is electrically connected to the positive electrode lead
9
of the electrode element
2
.
A safety valve used in a conventional nonaqueous electrolyte secondary battery will be described below with reference to
FIGS. 5 and 6
.
The configuration of the safety valve will be described below.
FIG. 5A
is a sectional view showing an action of the safety valve in a normal state of the conventional nonaqueous electrolyte secondary battery.
FIG. 5A
shows the upper portion of FIG.
4
.
FIG. 7A
is a plan view and a sectional view which show the configuration of the safety valve used in the conventional nonaqueous electrolyte secondary battery in a normal state. As shown in
FIG. 7A
, a linear thin portion
6
d
is formed almost along a circle centering on the projecting portion
6
e
. In addition, four thin portions
6
d
extending in the radial direction are formed outside the linear thin portion
6
c.
The disk
11
is fixed on the inner side of the safety valve
6
through a disk holder
12
.
The shape of the disk
11
will be described here.
FIG. 4B
is a plan view of a disk used in a conventional nonaqueous electrolyte secondary battery. In
FIG. 8B
, an edge portion
11
a
is a belt-like plate which partially constitutes the disk
11
and has a circular shape at the outside of the plate. The outer edge portion
11
a
itself is fixed to the gasket
8
to support the disk
11
as a whole.
A depressed portion
11
b
partially constitutes the disk
11
. The shape of the depressed portion
11
b
is a flat plate and is connected to the edge portion
11
a.
The disk
11
has a central hole
11
c.
The central hole
11
c
is a circular hole centering the symmetrical point of the disk
11
.
A peripheral hole
11
d
is an almost rectangular hole having a semicircular portion on the central hole
11
c
side, and the central axis of the peripheral hole
11
d
is in the radial direction.
The sub-disk
4
shown in
FIG. 4A
has a thin-disk-like shape, and is welded on the electrode element
2
of the disk
11
at the center of the disk
11
.
A positive electrode lead
9
is welded on the electrode element
2
of the sub-disk
4
. In this manner, the sub-disk
4
and the positive electrode lead
9
are electrically connected to each other.
The operation of the safety valve will be described below with reference to
FIGS. 5 and 6
. In this case, the safety valve
6
has two mechanisms, i.e., a current cut-off mechanism and a cleavage mechanism.
An operation in the current cut-off mechanism will be described below.
FIG. 5B
is a sectional view showing an action of a safety valve in a current cut-off state in the conventional nonaqueous electrolyte secondary battery.
When a gas is generated in the outer packaging can
1
for some reason, the internal pressure increases. At this time, the generated gas passes through a hole existing near the outer periphery of a disk
11
to pressurize the internal surface of the safety valve
6
. In this manner, the safety valve
6
is transformed outside.
In
FIG. 2A
, although the sub-disk
4
closes the central hole
11
c
of the disk
11
, the diameter of the sub-disk
4
is small. For this reason, the hole formed near the outer periphery of the disk
11
is not closed by the sub-disk
4
. Since the peripheral hole
11
d
of the disk
11
is not closed as described above, a gas existing in the battery can pass through the disk
11
. In contrast to this, since the safety valve
6
has no hole, the gas existing in the battery cannot be discharged outside, and an airtight state is kept.
In addition, at the welded portion between the projecting portion
6
a
of the safety valve
6
and the sub-disk
4
, the sub-disk
4
existing around the welded portion is torn by shearing force. In this manner, when the projecting portion
6
a
and the sub-disk
4
are separated from each other, an electric connection between the positive electrode lead
9
of the electrode element
2
and the lid
7
is cut. Here, the transformation of the safety valve
6
will be further described. As shown in
FIG. 2B
, when the safety valve
6
is transformed, the safety valve
6
is largely transformed at positions
6
k
and
6
l
. More specifically, the position
6
k
indicates the outer periphery of a flat region inside the safety valve
6
, and the position
6
l
indicates a position which is very close to the projecting portion
6
a
. The position
6
l
which is the bending point of these portions corresponds to the portion of the thin position
6
c
in FIG.
7
A. Since the portion of the thin portion
6
c
is mechanically weakest, the thin portion
6
c
is maximally transformed by pressure.
In addition, due to the transformation of the safety valve
6
, at the welded portion between the projecting portion
6
a
of the safety valve
6
and the sub-disk
4
, the sub-disk
4
existing around the welded portion is torn by shearing force. In this manner, when the projecting portion
6
a
and the sub-disk
4
are separated from each other,

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